Investments - Additional Information (Detail) - USD ($)	3 Months Ended
Mar. 26, 2016	Dec. 26, 2015
Schedule of Available-for-sale Securities [Line Items]
Investments maximum maturity period	5 years
Unrealized (loss) gain, net of unrealized gains/losses, on the investments in the bond portfolio	$ 137,000	$ (145,000)

Amount before tax of unrealized gain (loss) in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

No definition available.

Name:	us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainLossBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant